During the rainy season, the air becomes damp.
Scabies is a skin disease caused by mites.
乾燥 means dryness, the opposite condition to 湿, which refers to moisture or dampness.
The kanji 湿 carries the meaning of moisture or dampness. The medical sense is an extension of this idea, referring to the moist skin lesions associated with scabies.
damp; moist; humid
moisture absorption; absorbing moisture
wet process; wet type
wet (as in wet pleurisy)
moisture-proofing; damp-proofing
degree of humidity; dryness and wetness
low and damp; low-lying and humid
moisturizing; humidity retention
low and damp (land)
soil moisture
humidity
wet rubbing; ink rubbing using moistened paper
wet plate (photography)
fleshy fruit
hydrarch